Filter element and filter device

Abstract

A filter element includes a piezoelectric layer with a polarization axis direction, and division resonators provided at the piezoelectric layer. Each of the division resonators includes a functional electrode on the piezoelectric layer. Each of the functional electrodes includes high and low potential electrodes. When a direction parallel or substantially parallel to a direction in which the high and low potential electrodes face each other and oriented from the high-potential electrode toward the low-potential electrode is an inter-electrode direction, and a number of division resonators having the forward direction relationship is equal to a number of division resonators having the opposite direction relationship.

What is claimed is: 
     
         1 . A filter element comprising:
 a piezoelectric layer with a polarization axis direction; and   a plurality of division resonators including at least four division resonators provided at the piezoelectric layer and defined by an acoustic wave resonator divided in series and in parallel; wherein   each of the plurality of division resonators includes a functional electrode on the piezoelectric layer, each of the functional electrodes includes a high-potential electrode with a relatively high potential and a low-potential electrode with a relatively low potential;   when a direction parallel or substantially parallel to a direction in which the high-potential electrode and the low-potential electrode face each other and oriented from the high-potential electrode toward the low-potential electrode is defined as an inter-electrode direction, and when a relationship in which a component of the polarization axis direction parallel or substantially parallel to the inter-electrode direction and the inter-electrode direction are in a same direction is defined as a forward direction relationship and a relationship in which the component of the polarization axis direction parallel or substantially parallel to the inter-electrode direction and the inter-electrode direction are in opposite directions is defined as an opposite direction relationship, a number of division resonators with the forward direction relationship is equal to a number of division resonators with the opposite direction relationship among the plurality of division resonators; and   the plurality of division resonators include a first pair of resonators connected in parallel and a second pair of resonators connected in parallel, and the first pair of resonators and the second pair of resonators are connected in series.   
     
     
         2 . The filter element according to  claim 1 , wherein
 the plurality of division resonators are each defined as different stages based on an order of connecting the division resonators from a high potential side; and   among the plurality of division resonators, a number of division resonators in a same stage is two, and among the two division resonators in the same stage, one has the forward direction relationship and another has the opposite direction relationship.   
     
     
         3 . The filter element according to  claim 2 , wherein
 the plurality of division resonators each include an excitation region where an acoustic wave is excited; and   areas of the excitation regions of the two division resonators in the same stage are equal or substantially equal to each other.   
     
     
         4 . The filter element according to  claim 1 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, and a third division resonator and a fourth division resonator connected in common to both of the first division resonator and the second division resonator. 
     
     
         5 . The filter element according to  claim 4 , wherein the plurality of division resonators include a fifth division resonator connected to at least the third division resonator, and a sixth division resonator connected to at least the fourth division resonator. 
     
     
         6 . The filter element according to  claim 1 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, a third division resonator connected in series with the first division resonator, and a fourth division resonator connected in series with the second division resonator. 
     
     
         7 . The filter element according to  claim 1 , wherein, in each of the plurality of division resonators, the high-potential electrode and the low-potential electrode face each other with the piezoelectric layer interposed therebetween. 
     
     
         8 . The filter element according to  claim 1 , wherein
 the functional electrode of each of the plurality of division resonators is an IDT electrode; and   each of the IDT electrodes includes the high-potential electrode and the low-potential electrode, each of the high-potential electrodes includes a first busbar and each of the low-potential electrodes includes a second busbar, and the inter-electrode direction is parallel or substantially parallel to a direction in which the first busbar and the second busbar face each other and is oriented from the first busbar toward the second busbar.   
     
     
         9 . The filter element according to  claim 1 , wherein the piezoelectric layer is a lithium tantalate layer or a lithium niobate layer. 
     
     
         10 . A ladder filter comprising:
 a plurality of resonators in a series arm and a parallel arm; wherein   the filter element according to  claim 1  is provided in the series arm.   
     
     
         11 . The ladder filter according to  claim 10 , wherein
 the plurality of division resonators are each defined as different stages based on an order of connecting the division resonators from a high potential side; and   among the plurality of division resonators, a number of division resonators in a same stage is two, and among the two division resonators in the same stage, one has the forward direction relationship and another has the opposite direction relationship.   
     
     
         12 . The ladder filter according to  claim 11 , wherein
 the plurality of division resonators each include an excitation region where an acoustic wave is excited; and   areas of the excitation regions of the two division resonators in the same stage are equal or substantially equal to each other.   
     
     
         13 . The ladder filter according to  claim 10 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, and a third division resonator and a fourth division resonator connected in common to both of the first division resonator and the second division resonator. 
     
     
         14 . The ladder filter according to  claim 13 , wherein the plurality of division resonators include a fifth division resonator connected to at least the third division resonator, and a sixth division resonator connected to at least the fourth division resonator. 
     
     
         15 . The ladder filter according to  claim 10 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, a third division resonator connected in series with the first division resonator, and a fourth division resonator connected in series with the second division resonator. 
     
     
         16 . A ladder filter comprising:
 a plurality of resonators in a series arm and a parallel arm; wherein   the filter element according to  claim 1  is provided in the parallel arm.   
     
     
         17 . The ladder filter according to  claim 16 , wherein
 the plurality of division resonators are each defined as different stages based on an order of connecting the division resonators from a high potential side; and   among the plurality of division resonators, a number of division resonators in a same stage is two, and among the two division resonators in the same stage, one has the forward direction relationship and another has the opposite direction relationship.   
     
     
         18 . The ladder filter according to  claim 17 , wherein
 the plurality of division resonators each include an excitation region where an acoustic wave is excited; and   areas of the excitation regions of the two division resonators in the same stage are equal or substantially equal to each other.   
     
     
         19 . The ladder filter according to  claim 16 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, and a third division resonator and a fourth division resonator connected in common to both of the first division resonator and the second division resonator. 
     
     
         20 . The ladder filter according to  claim 16 , wherein the plurality of division resonators include a first division resonator and a second division resonator connected in common to a same potential, a third division resonator connected in series with the first division resonator, and a fourth division resonator connected in series with the second division resonator.